No. 1.] ORIGIN OF HUMAN MONSTERS. 21 
ported especially by the numerous investigations in experi- 
mental embryology, many of which are also at the same time 
investigations in experimental teratology. For this reason I 
shall consider briefly the recent work upon the production of 
merosomatous monsters. 
Liruium Emsryos anp NopuLar Forms 
IN CHICKS AND IN MAN. 
Comparative teratology gives ample testimony to explain 
the production of double monsters, and it is now clear how 
they may be produced in man. But when the study is ex- 
tended to merosomatous terata great difficulties arise in making 
comparisons between the large number of experimental mon- 
sters in lower animals, the pathological embryos which I have 
studied, and finished monsters at the end of pregnancy. The 
endless literature upon these subjects is very difficult to blend 
into a continuous story on account of the various terminol- 
ogies used by the different writers. However, I hope to draw 
some satisfactory lines through it, being guided by compara- 
tive anatomy and embryology. © 
The immense number of experiments performed upon the 
eggs of different species of animals has given the greatest 
variety of monsters of very irregular form, and extremely 
difficult to interpret properly in the light of our present knowl- 
edge of embryology. Quite recently our distinguished tera- 
tologist, Morgan, has presented this problem in a new light 
in his series of studies on the relation between normal and 
abnormal development of the embryo of the frog. No doubt 
scientific investigations like these of Morgan will soon clear 
up many of the questions in teratology which have perplexed 
us so long. It may be noted that new kinds of monsters are 
constantly being produced by the experimental teratologist, 
one of the most interesting being that known as the lithium 
larva. 
*Morgan, Ten Studies in Roux’s Archiv, Vols. XV-XIX, 1902-1905. 
